The present invention relates generally to medical devices and more particularly to devices for accessing a lumen inside a body.
One type of minimally invasive medical procedure is hemodialysis. Hemodialysis is the most common treatment for permanent or chronic kidney failure. Kidney failure results in the body's inability to filter toxins, fluids, and waste from the blood, resulting in a potentially life-threatening build-up of these substances. Among the substances that often build up as a result of kidney failure are urea, potassium, and phosphates. When undergoing hemodialysis, a person suffering from kidney failure utilizes a machine to perform the filtering function normally performed by the kidneys.
Persons requiring hemodialysis generally must use a dialysis machine for several hours at a time. Treatment must occur several days each week. During treatment, a needle typically is used to draw blood, usually from an artery. The blood is run through the dialysis machine, which filters out harmful toxins, excess fluids, and wastes. The filtered blood is then returned to the body via a second needle inserted at a different point in the vascular system, preferably a vein. Blood must be drawn from a vessel with a high rate of flow because the dialysis machine processes blood at a high rate of speed. Using a vessel with an insufficient rate of blood flow may cause the vessel to collapse as the dialysis machine draws blood out of the body.
In order to insure that a high blood flow rate is present, blood is often drawn from an arteriovenous (AV) fistula. AV fistulas include autogenous fistulas, which are composed of naturally occurring blood vessels, and non-autogenous fistulas, which are made of synthetic materials or non-native blood vessels. An autogenous fistula consists of an artery and a vein that are directly connected together, allowing blood to bypass smaller capillaries. Fistulas are most often surgically created in the arm, but may be created elsewhere in the body. Blood flow through a fistula is generally greater than the blood flow through a naturally occurring artery or vein, maximizing the amount of blood that may be filtered by the dialysis machine in a period of time. Non-autogenous fistulas are created by using an artificial graft of biocompatible tubing or a non-native blood vessel to create a high blood flow vascular access site. Non-autogenous fistulas are commonly referred to as “grafts.” Common materials used for non-autogenous fistulas (grafts) include polytetrafluorethylene (PTFE), silicone, and biologic materials. For example, a graft may be created using a natural vessel harvested from another part of the body, such as the leg, and used to connect an artery and a vein together in a patient's arm. Alternatively, a bovine or sheep vessel may be utilized. After they are surgically connected, both autogenous fistulas and non-autogenous fistulas (grafts) take several weeks to mature to the point that the vascular access site can be used for hemodialysis. Once mature, a needle for withdrawing blood is typically inserted in the arterial side of vascular access site and a needle for returning the filtered blood is inserted into the venous side of the vascular access site.
A patient without a mature vascular access site may utilize central venous hemodialysis. In this type of hemodialysis, blood is drawn from a large blood vessel in the chest or neck such as the vena cava, internal jugular vein, subclavian vein, or femoral vein. For central venous hemodialysis, a single plastic catheter with two lumens is typically used. This type of hemodialysis allows less blood flow than a fistula. It is also associated with a high rate of infection.
In most forms of hemodialysis, due to the large amount of blood that is removed, two large hypodermic needles are typically used. One needle is used to withdraw blood, while the second is used to return the blood to the body. These needles must remain in place for hours at a time and they must be used multiple times weekly, often for years. The needles normally must remain inside the blood vessel for long periods of time, during which time the patient may move or shift positions, causing the needle to irritate the blood vessel walls. Irritation from the needles may cause scar tissue to form within the lumen of the blood vessel or fistula. Over time, scar tissue may build up, narrowing the blood vessel or fistula. This narrowing of the vascular system may also be referred to as a stenosis. Stenosis of a blood vessel or fistula may result in thrombosis, i.e., clotting of the blood vessels. Thrombosis may render a particular blood vessel or fistula unusable. The repeated use of needles to penetrate the vessel or fistula may also weaken the vascular access site, causing aneurysms and pseudoaneurysms. An aneurysm is an abnormal blood-filled dilation of a blood vessel. A pseudoaneurysm is an abnormal twisting or pouching of a blood vessel that resembles a true aneurysm in appearance. Blood slows and collects in aneurysms and pseudoaneurysms, increasing the risk that it will coagulate and result in thrombosis.
Stenosis, aneurysms, and pseudoaneurysms, and the resulting thrombosis, can reduce the longevity of a vascular access site. When a vascular access site becomes unusable, a patient must choose between having a doctor surgically thrombectomize the vascular access site to clear the thrombosis or using an alternate site. Studies have shown that over 70% of vascular access sites that are thrombectomized become clotted again within six months. Because of the high rate of reoccurrence, when a fistula becomes unusable, patients often must switch to central venous hemodialysis until a new fistula can be surgically created and has matured. These surgeries are expensive and time consuming. In addition, with every surgery, patients undergo a risk of infection and other potentially life-threatening complications.